Fix faulty io net error handling code in posix BSP

Basically, when the SDK allocates the structure in which it will
store the socket descriptor it opens when connecting to the iotcore
server, it initializes it to 0. If during the process of creating the
socket, the posix BSP routine (iotc_bsp_io_net_socket_connect) that
creates the socket can’t resolve the iotcore server name, it returns
an error (leaving the socket descriptor field initialized to 0). In
turn, the io net routine (iotc_io_net_layer_connect) that itself
called iotc_bsp_io_net_socket_connect, on seeing the error, will then
execute its error handling code that itself ends up calling the io
net routine iotc_io_net_layer_close_externally that then calls the
posix BSP iotc_bsp_io_net_close_socket routine. The posix BSP
iotc_bsp_io_net_close_socket routine then blindly closes socket
descriptor 0 (since this is what the data structure tracking the
socket descriptor is still initialized to since no socket was ever
successfully opened).

Files modified:

src/bsp/platform/posix/iotc_bsp_io_net_posix.c

- always set *iotc_socket to -1 before attempting to connect or after
  closing the socket and always check that *iotc_socket is not -1
  before attempting to close it in iotc_bsp_io_net_close_socket().

Author: pnfisher

src/bsp/platform/posix/iotc_bsp_io_net_posix.c

@@ -49,6 +49,13 @@ iotc_bsp_io_net_state_t iotc_bsp_io_net_socket_connect(
   hints.ai_flags = 0;
   hints.ai_protocol = 0;
 
+  // in case of error, we want *iotc_socket initialized to a non-valid
+  // value so that iotc_bsp_io_net_close_socket can check before
+  // closing a socket to ensure that the socket was genuinely opened;
+  // otherwise iotc_bsp_io_net_close_socket can be at risk of
+  // incorrectly closing STDIN_FILENO
+  *iotc_socket = -1;
+
   // Address resolution.
   status = getaddrinfo(host, NULL, &hints, &result);
   if (0 != status) {
@@ -90,6 +97,7 @@ iotc_bsp_io_net_state_t iotc_bsp_io_net_socket_connect(
         return IOTC_BSP_IO_NET_STATE_OK;
       } else {
         close(*iotc_socket);
+        *iotc_socket = -1;
       }
     }
   }
@@ -200,11 +208,16 @@ iotc_bsp_io_net_state_t iotc_bsp_io_net_close_socket(
     return IOTC_BSP_IO_NET_STATE_ERROR;
   }
 
+  if (*iotc_socket < 0)
+	  // no need to close a socket that was never opened in the first
+	  // place
+	  return IOTC_BSP_IO_NET_STATE_OK;
+
   shutdown(*iotc_socket, SHUT_RDWR);
 
   close(*iotc_socket);
 
-  *iotc_socket = 0;
+  *iotc_socket = -1;
 
   return IOTC_BSP_IO_NET_STATE_OK;
 }